使用 Ruby 实现 HTTPS 证书/公钥固定

Question

我有自己的 HTTPS 服务，我正在通过另一个 Ruby 应用程序与之通信。我想在我的应用程序仓库中的一个已知时间点保存它的公钥证书，并将服务发送给我的公钥与存储的副本进行比较。要在外部服务器上安装证书，我可能必须将其转换为某种格式，因此服务器发送的文件不会相同。

我想对特定的公钥进行各种证书固定。我需要使用 OpenSSL 比较证书的哪些字段，以验证我从服务收到的 PK 是否与从服务器收到的相同？

我想 CN 和签名至少必须匹配。还有什么需要检查才能知道我拥有的公共证书与我收到的完全匹配（即相同的证书）？也许 OSSL 有一个内置的功能？

Answer 1

好的，在对 OpenSSL 进行了一番探讨之后，我已经了解了以下公钥固定的简单实现。其实很简单。不幸的是，我没有看到流行的 HTTP 中间件库（如 Faraday 和 HTTPClient）提供对 verify_callback 的访问权限，这实际上在每个 OpenSSL 会话中都可用。

在此示例中，如果 PK 与您之前固定的 PK 不匹配，会话将立即终止。请注意，不会使用 OpenSSL::SSL::VERIFY_NONE 调用该块（无论如何都不应该使用它）。

require 'net/http'
require 'openssl'

# Grab the cert received out of band by pigeon post
cert_code = File.read 'github.com.cer'
downloaded_cert = OpenSSL::X509::Certificate.new(cert_code)

# Tells us whether the private keys on the passed certificates match
# and use the same algo
def same_public_key?(ref_cert, actual_cert)
  pkr, pka = ref_cert.public_key, actual_cert.public_key

  # First check if the public keys use the same crypto...
  return false unless pkr.class == pka.class
  # ...and then - that they have the same contents
  return false unless pkr.to_pem == pka.to_pem

  true
end

# Configure a new HTTP object
http = Net::HTTP.new('github.com', 443)
http.use_ssl = true

# We will verify against our CAs in the root store, and with VERIFY_NONE
# the verify_callback will not fire at all, which defeats the purpose.
http.verify_mode = OpenSSL::SSL::VERIFY_PEER

# verify_callback will be called once for every certificate in the chain,
# starting with the top level certificate and ending with the actual certificate
# presented by the server we are contacting. Returning false from that callback
# will terminate the TLS session. Exceptions within the block will be suppressed.
#
# Citing the Ruby OpenSSL docs:
#
# A callback for additional certificate verification. The callback is invoked 
# for each certificate in the chain.
# 
# The callback is invoked with two values. preverify_ok indicates if the verification 
# was passed (true) or not (false). store_context is an OpenSSL::X509::StoreContext
# containing the context used for certificate verification.
# 
# If the callback returns false verification is stopped.
http.verify_callback = lambda do | preverify_ok, cert_store |
  return false unless preverify_ok

  # We only want to verify once, and fail the first time the callback
  # is invoked (as opposed to checking only the last time it's called).
  # Therefore we get at the whole authorization chain.
  # The end certificate is at the beginning of the chain (the certificate
  # for the host we are talking to)
  end_cert = cert_store.chain[0]

  # Only perform the checks if the current cert is the end certificate
  # in the chain. We can compare using the DER representation
  # (OpenSSL::X509::Certificate objects are not comparable, and for 
  # a good reason). If we don't we are going to perform the verification
  # many times - once per certificate in the chain of trust, which is wasteful
  return true unless end_cert.to_der == cert_store.current_cert.to_der

  # And verify the public key.
  same_public_key?(end_cert, downloaded_cert)
end

# This request will fail if the cert doesn't match
res = http.get '/'

如果您想进行整个证书固定并且证书不受轮换，您可以使用证书指纹：

def same_cert_fingerprint?(ref, actual)
  OpenSSL::Digest::SHA256.hexdigest(ref.to_der) ==  OpenSSL::Digest::SHA256.hexdigest(actual.to_der)
end

编辑：看起来至少 excon 最近实现了这个：

https://github.com/geemus/excon/commit/12437b79bad2a0e51bb4ac5b79c155eb88128245

Answer 2

作为@Julik 回答的后续，RestClient (https://github.com/rest-client/rest-client) 自 1.6.8 起支持verify_callback。

# The value of ssl_verify_callback is assigned to Net::HTTP#verify_callback.
RestClient::Resource.new(uri, ssl_verify_callback: ...).get